How to prevent and eliminate aphid infestations

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Systemic insecticides, including the neonicotinoid-based insecticides imidacloprid (Marathon®), thiamethoxam (Flagship®), acetamiprid (TriStar®), dinotefuran (Safari®), and clothianidin (Celero®), effectively control aphids for extended periods of time when applied early in the cropping cycle. The same is true of the selective feeding blockers, pymetrozine (Endeavor®) and flonicamid (Aria®). A number of insecticides have both translaminar and systemic properties. See the current New England Recommendation guide for more information.

Preventive Strategies

  • Practice good sanitation, such as removing discarded plant material and eliminating weeds around plant production areas. Weed host plants often serve as reservoirs for migrating or ant carried aphids.
  • Avoid excessive amounts of nitrogen fertilizer which promote soft plant tissue. New, soft plant tissue promote higher aphid populations.
  • Use physical control methods if appropriate. These include screens or other barriers. Screens are especially important in stock plant production areas to reduce the threat of virus transmission.
  • Thoroughly inspect all incoming plant material and spot treat if necessary.

 

Aphid Parasitoids

In general, parasitoids are more effective than predators in reducing aphid populations, although parasitoids may fail to provide acceptable control under warm conditions or at times when aphid populations tend to increase rapidly. Four parasitoids are commercially available. Aphid parasitoids are host-specific in terms of the aphid species they attack. For example, Aphidius ervi attacks foxglove aphid, while Aphidius colemani attacks both green peach and melon aphids. Mixtures of different parasitoid species are commercially available and should be used when multiple aphid species are present. Parasitoids are shipped either as adults or ‘aphid mummies’ from which parasitoid adults soon emerge. To increase the parasitoids’ effectiveness, place small groups of the aphid mummies in cups near aphid colonies. Do not let these aphid mummies get wet. Release rates may vary depending on the parasitoid species. Containers often contain approximately 250 aphid mummies, which can treat 5,000 ft2 at the high release rate or 25,000 ft2 at the low release rate.

Greenhouse temperatures should be 65-77F (18-25C), with 70-85% relative humidity. Aphid parasitoids must be applied preventively to suppress aphid populations. They are less effective when aphid populations are high and already causing plant damage. Release parasitoids on a regular basis to sustain their populations during the growing season. Remove yellow sticky cards before releasing parasitoids, as sticky cards attract and capture parasitoids. When scouting, look for aphid mummies that have circular holes on one end. These are the exit holes created by adult parasitoids during emergence. Aphid parasitoids are sensitive to pest control materials. For example, direct sprays and one-day old residues of kinoprene (Enstar II®) are harmful to A. colemani . Direct applications of spinosad (Conserve®) are also toxic to A. colemani.

Release parasitoids preventively on crops you know are susceptible to aphids, so that the parasitoids will be present when aphids are first noticed. Also, identify aphids to species before ordering parasitoids, since parasitoids are selective in the aphid species they attack. For example, release Aphidius colmani for green peach aphid, and Aphidius ervi or Aphelinus abdominalis for foxglove or potato aphid. Some biological control suppliers sell mixtures of parasitoid species, which may be useful when several aphid species are present in the greenhouse simultaneously. Banker plant systems may be useful in controlling aphids and reducing the costs associated with applying pest control materials. Banker plants support colonies of aphids that are not greenhouse crop pests, along with parasitoids. Information on banker plants is available at:http://www.negreenhouseupdate.info/ [5] (type in banker plant in the search tool for details). Also see the fact sheet: Aphid Banker Plant System for Greenhouse IPM, Step by Step [6] (from UVM and Biobest) If aphids are already abundant then you must reduce their numbers before releasing natural enemies. You can reduce aphid populations by applying the pest control material pymetrozine (Endeavor®), which kills insects with piercing-sucking mouthparts, including aphids. Endeavor® has been demonstrated to be compatible with aphid and whitefly parasitoids, and predatory mites used to control thrips and spider mites. Do not attempt to suppress high aphid populations with predators, as this is typically not effective.